Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart. However, the appended claims are not intended to be limited to any specific example or embodiment described herein.
Pacemaker leads form the electrical connection between the cardiac pacemaker pulse generator and the heart tissue which is to be stimulated. As is well known, the leads connecting such pacemakers with the heart may be used for pacing, or for sensing electrical signals produced by the heart, or for both pacing and sensing in which case a single lead serves as a bi-directional pulse transmission link between the pacemaker and the heart. An endocardial type lead, that is, a lead which is inserted into a vein and guided therethrough into a cavity of the heart, includes at its distal end an electrode designed to contact the endocardium, the tissue lining the inside of the heart. The lead further includes a proximal end having a connector pin adapted to be received by a mating socket in the pacemaker. A flexible, coil conductor surrounded by an insulating tube or sheath typically couples the connector pin at the proximal end and the electrode at the distal end.
The implantable cardiac stimulator with which the present lead invention is concerned may take the form of a pacemaker capable of pacing and sensing in at least one chamber of the heart. Indeed, the present invention, may relate to a programmable dual chamber pacemaker wherein the basic configuration of the pacemaker, e.g. unipolar or bipolar, can be changed, including the grounding configuration and ground potentials used within the pacemaker.
Generally, a heart stimulator, commonly known as a “pacemaker” or “pacer”, uses one or two flexible leads having one end connected to the pacer and the other end connected to electrodes placed in close proximity to the heart. These leads are used to stimulate or pace the heart. Also, these leads are used to sense the heart activity by picking up electrical signals from the heart.
In order to properly pace or sense, the pacer has to be able to deliver a stimulating pulse to the heart or sense an electrical signal from the heart, and this requires that there be an electrical return path. If, within a given heart chamber, a unipolar lead is used—containing a single conductor—the return path is the conductive body tissue and fluids. The return path is connected to the pacer by connecting the pacer electrical common or ground to the pacer metal enclosure, typically referred to as the pacer case or housing. The case, in turn, makes contact with the body tissue and/or fluids.
An alternative solution to using a unipolar lead in a given heart chamber is to use a double lead/electrode in the heart chamber, known as a bipolar lead. In a bipolar lead, a second conductor is spiraled over and insulated from a first conductor along the length of the lead. At the distal end of the lead, one of the conductors is connected to a first electrode, referred to as the “tip” electrode, and the second conductor is connected to a second electrode, referred to as a “ring” electrode. The ring electrode is generally situated about 8 to 20 mm from the tip electrode. The tip electrode is typically placed in contact with heart tissue, while the ring electrode is in electrical contact with the blood. Because both body tissue and fluids are conductive, the ring electrode of a bipolar lead, in contact with the body fluids, serves as an electrical return for both pacing and sensing.
As indicated, pacing or sensing using the pacer case or enclosure as part of the electrical return path is known as unipolar pacing or sensing. Pacing or sensing using the lead ring electrode and associated lead conductor as the electrical return path is known as bipolar pacing or sensing. There are numerous factors to consider when deciding whether unipolar or bipolar pacing and/or sensing should be used. Bipolar pacing has, in general, the advantage of requiring less energy than unipolar pacing. Further, bipolar sensing is less prone to crosstalk and myopotential sensing than is unipolar sensing. Crosstalk generally refers to a pacer mistakenly sensing a heart activity in one heart chamber immediately after the other chamber is paced. Bipolar sensing reduces crosstalk resulting from a pacing stimulus in the opposite chamber. Bipolar pacing is preferred if pectoral or diaphragmatic stimulation occurs.
Unipolar pacing and sensing offers the advantage, in general, of simpler circuitry within the pacemaker and a smaller diameter lead. Some physicians prefer unipolar over bipolar pacing and/or sensing as a function of other implantation and heart conditions. Depending on the lead orientation, unipolar sensing may be preferable to bipolar sensing.
Cardiac rhythm management (CRM) is a growing yet maturing industry in which product design is becoming less differentiated. As this industry matures and profit margins tighten, increasing importance lies in making quality products that are low cost and easily produced. A commonly produced product in CRM is a “J” configured lead that delivers electrical pulses from the generator to the atrium of the heart. This “J” lead achieves its “J” shape through the use of pre-shaped components. A new design that reduces the number of pre-shaped components and improves manufacturing ease is needed to lower costs and improve manufacturability.
A new “J” lead design that is low cost and more easily produced is accomplished by reducing the number of pre-shaped components. The new design of the invention uses fewer pre-shaped components, thereby improving manufacturability and lowering cost.
The common industry “J” lead design employs a “J” formed outer tube and a “J” formed outer coil conductor. The thin and flexible inner coil conductor and inner tube are both in a straight configuration. To form each “J” shaped component adds cost, and in the case of silicone tubing can more than double the price. Separate from component cost, multiple pre-formed “J” components require alignment of each during the manufacturing process. If the “J” formed outer tubing and coil conductor are not aligned properly, the assembled lead will not have the correct “J” configuration.
The “J” lead design of the invention uses a single pre-shaped looped outer coil conductor with a straight inner coil conductor, inner tube, and outer tube. The use of these components results in a final “J” lead that is generally similar to the final “J” lead, but with cost and manufacturability advantages. The straight outer tubing of the looped coil conductor design is significantly less expensive than the “J” formed tube used in a conventional design. In addition to the cost advantage gained in these high volume products, a single looped coil conductor design allows for a more easily assembled product.
This looped coil conductor “J” lead design thus gives the assignee of this technology a production and cost advantage at a time when producing quality lead products cheaper and faster is of ever increasing importance.
A couple of patents are considered to be generally illustrative of the prior art. U.S. Pat. No. 4,488,561 to Doring discloses a body implantable lead which may be easily provided with a desired predetermined curve or bend. As such, the disclosed invention allows for a pacing lead convertible from use in the ventricle to use in the atrium or other desired location. A stylet wire having a generally straight configuration is removably mounted within a concentric memory coil conductor tending to assume the desired curved shape. The stylet and memory coil conductor may be inserted together within the lead body, the stylet maintaining the memory coil conductor in a generally straight configuration. After removal of the stylet, the memory coil conductor urges the lead body to assume the desired predetermined curve, facilitating use of the lead in the atrium.
U.S. Patent Application Publication No. US 2002/0049485 published on Apr. 25, 2002 discloses an elongated coronary vein lead having a variable stiffness lead body most preferably adapted to be advanced into a selected coronary vein for delivering a pacing or defibrillation signal to a predetermined region of a patient's heart, such as the left ventricle. The variable stiffness lead body enhances the ability of the lead to be retained in a coronary vein after the lead has been implanted.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.